The use of drilling mud is an essential adjunct to the rotary drilling procedures, which procedures date back to the turn of the century. A highly viscous fluid material called "mud" (primarily because in the early days it consisted of soil and water) is forced down the drill stringer under high pressure and jetted out through the drill bit to cool as well as clean the bit. The mud material returns upwardly through the annulus about the drilling string, thereby carrying away loose material and in some instances adding additional support against potential collapse of the hole strata.
Because of the high viscosity of the mud and the high pressure and flow requirements, particularly for deep well drilling, piston or plunger type pumps have been found the most serviceable and satisfactory. Very early pumps were steam driven reciprocating pistons in a liner. Over the years the simplex pump was developed and was followed by a duplex, and more recently, a triplex pump which was placed into service in about 1953. The duplex and triplex pumps are in wide use today and typically comprise an aggregation of bull gears, bearings, seals and other high maintenance inner workings. Pumps of this type typically move at high speeds and have a very short piston stroke, the inevitable consequence of which is high liner and valve maintenance.
The pump to which the present invention is adapted is in reality a series of pump assemblies, plumbed in parallel each of which is relatively simple, involving a minimum of moving parts. The pump, by virtue of its construction, is capable of lower operating speeds than those now in use, with a commensurate lower maintenance cost. Each of the pumps comprises a piston operating within an elongated liner with a rod interconnecting the piston to a fluid drive motor which is reciprocated to move the piston through a suction stroke to draw viscous mud into the liner and a return or discharge stroke to force the mud under pressure to the drill string.
In order to effectively use pumps of the type described, all of the pump assemblies which comprise the whole must be properly sequenced and sychronized in order to avoid pressure surges in the discharge line which, if permitted, could result in severe damage to the entire mud circulation system, including the well hole.
It is characteristic that the type of pump to which the present invention pertains to lose synchronization when pump operating speed is adjusted, and the present invention is particularly useful in overcoming this undesireable characteristic through its ability to continuously monitor variations in fluid flow which equates to pump speed changes and to automatically adjust to such changes to maintain proper sequencing.
Triplex and duplex mud pumps currently in use recognize the problem and even though they are mechanically synchronized, expensive pulsation dampeners are customarily used on the discharge side to avoid surge and pressure peaks. Additional force feed equipment is needed to assist the pumps in the process of ingesting mud during the suction stroke. A significant feature of the present invention is that a control system is provided which insures proper sequencing through the full range of operating speeds, thereby permitting the delivery to the drill string of a highly uniform mud flow rate and pressure without recourse to ancillary equipment such as pulsation dampeners and forced suction flooding. Thus, it is that a major contribution to rotary drilling is made by the present invention which permits the use of a plurality of fluid driven pumps, connected in parallel by providing means for automatically and continuously sequencing each pump with the others to permit delivery to the drill string of mud at a pre-determined and modulated flow rate and pressure.